Magnetic excitations in the spin chain candidate ${\mathrm{Sr}}_2{\mathrm{V}}_3{\mathrm{O}}_9$ have been investigated by inelastic neutron scattering on a single crystal sample. A spinon continuum with a bandwidth of $\sim 22$ meV is observed along the chain formed by alternating magnetic ${\mathrm{V}}^{4+}$ and nonmagnetic ${\mathrm{V}}^{5+}$ ions, which reveals the importance of the orbital degree of freedom in determining the chain axis as identified by prior electronic structure calculations. Incipient magnetic Bragg peaks due to weak ferromagnetic interchain couplings emerge when approaching the magnetic transition at $T_N\sim 5.3$ K, while the excitations remain gapless within the instrumental resolution. Comparisons to the Bethe ansatz, density matrix renormalization group calculations, and effective field theories confirm ${\mathrm{Sr}}_2{\mathrm{V}}_3{\mathrm{O}}_9$ as a host of weakly coupled $S=1/2$ chains dominated by antiferromagnetic intrachain interactions of $\sim 7.1$(1) meV.

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• 1-dimensional spin chains
• Bethe ansatz
• Inelastic neutron scattering
• Neutron scattering
• Numerical techniques